JP6370885B2 - Electrode including a coating layer for preventing reaction with electrolyte - Google Patents

Description

  The present invention relates to an electrode on which a coating layer that suppresses a reaction with an electrolytic solution is formed.

  With the development of technology and increasing demand for mobile devices, the demand for secondary batteries as energy sources has increased rapidly. Among such secondary batteries, it has a high energy density and voltage, has a long cycle life, Lithium secondary batteries with a low self-discharge rate have been commercialized and widely used.

In such lithium secondary batteries, lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used. In addition, lithium-containing manganese oxides such as LiMnO ₂ having a layered crystal structure and LiMn ₂ O _{4 having} a spinel crystal structure are used. And the use of lithium-containing nickel oxide (LiNiO ₂ ) is also being considered.

In particular, lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have the advantage that they use abundant resources and use environmentally friendly manganese as a raw material, so that a positive electrode active that can replace LiCoO ₂ is used. Has attracted a lot of interest as a substance

However, lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ react with the electrolyte solution as the cycle continues, and the electrolyte solution is rapidly depleted, resulting in a decrease in the life and cycle characteristics of the secondary battery. There's a problem. In addition, the volume of the secondary battery expands due to a large amount of gas generation and manganese elution.

On the other hand, lithium-containing manganese oxide includes Li ₂ MnO _{3 in} addition to LiMnO ₂ and LiMn ₂ O ₄ . Li ₂ MnO ₃ is very excellent in structural stability, but is electrochemically inactive, and cannot itself be used as a positive electrode active material for a secondary battery. Accordingly, some prior arts present a technique for using Li ₂ MnO ₃ as a positive electrode active material by forming a solid solution with LiMO ₂ (M = Co, Ni, Ni _0.5 Mn _0.5 , Mn). ing. Such a solid solution positive electrode active material is liable to react with the electrolyte at a high voltage because Li and O are detached from the crystal structure at a high voltage of 4.4 V and become electrochemically active. The problem that the battery is depleted and the volume of the secondary battery expands cannot be solved.

  Therefore, there is a high need for a technique that can suppress the reaction between the active material and the electrolyte and can significantly improve the life and cycle of the secondary battery.

  An object of the present invention is to solve the above-described problems of the prior art and technical problems that have been requested from the past.

As a result of intensive research and various experiments, the inventors of the present application formed a coating layer containing aluminum (Al) and / or alumina (Al ₂ O ₃ ) on the electrode mixture layer as described later. As a result, it was confirmed that the desired effect could be achieved, and the present invention was completed.

Therefore, in the electrode for a secondary battery according to the present invention, an electrode mixture layer containing an electrode active material is applied on an electrode current collector, and aluminum (Al) and / or on the electrode mixture layer. A coating layer containing alumina (Al ₂ O ₃ ) is formed.

  Such a coating layer can suppress the reaction of the electrode active material with the electrolytic solution, and thus can solve the conventional problems described above.

  The coating layer may be formed to a thickness of 0.5 nm to 100 nm, and the coating layer may be formed on all or part of the surface of the electrode mixture layer.

  Here, when the coating layer is 0.5 nm or less, the effect of the coating layer is extremely small. When the coating layer is 100 nm or more, rather, the movement of the lithium ion is limited to lower the electrode performance. There is.

  The coating layer may be formed on all or part of the surface of the electrode mixture layer. Specifically, the coating layer may be formed with an area of 100% to 50% of the surface area of the electrode mixture layer. Good.

  When the area of the coating layer is 50% or less, the reaction distance between oxygen and aluminum increases, and not only the generated oxygen cannot be captured but also the oxidation reaction of the electrolyte solution at a high voltage. It is not preferable because it cannot be suppressed.

  In one non-limiting example, the coating layer can include both aluminum and alumina.

  In this case, the coating layer may have a structure in which aluminum and alumina form a gradient with respect to the thickness direction.

  As an example of the structure, the aluminum content of the coating layer may decrease from the contact surface with the electrode mixture layer to the surface of the electrode, and the alumina content may increase.

  Meanwhile, as still another example of the structure, the aluminum content of the coating layer decreases from the center of the coating layer toward the contact surface with the electrode mixture layer and the surface of the electrode, and the alumina content increases. May be.

  In one non-limiting example, the coating layer can be uniformly formed through electrolysis, where the aluminum precursor is ionized with a solution for electrolysis and the electrolytic electrode is converted to aluminum metal. Can be reduced.

  The electrolytic electrode is a reduction electrode for depositing aluminum metal on the surface, and is distinguished from the secondary battery electrode according to the present invention.

  The solution is a stable material that can dissolve an aluminum precursor and is not oxidized / reduced at less than 4.6 V and less than 1.5 V compared to lithium, and more specifically, a cyclic carbonate, a cyclic ester It may be one or more solvents selected from (cyclic esters), linear carbonates or linear esters.

The aluminum precursor may be AlCl ₃ , but is not limited thereto.

In one non-limiting example, the electrolysis may be performed through a catalyst, and examples of the catalyst include a ZnCl ₂ system, a CoCl ₂ system, a MnCl ₂ system, a NiCl ₂ system, and a SnCl ₂ system. The catalyst may be one or more selected from the group, but is not limited thereto.

  Meanwhile, the electrode may be a positive electrode, and the electrode active material may include a lithium transition metal oxide represented by the following chemical formula 1 or 2.

_{Li x M y Mn 2-y} O 4-z A z (1)
In the above formula,
M is selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti, and Bi 1 Two or more elements,
A is one or more anions of -1 or -2 valence,
0.9 ≦ x ≦ 1.2, 0 <y <2, and 0 ≦ z <0.2.
(1-x) LiM′O _2-y A _y -xLi ₂ MnO _{3-y ′} A _{y ′} (2)
In the above formula,
M ′ is Mn _a M _b
M _b is one or more selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn, and two-period transition metals,
A is one or more selected from the group consisting of PO ₄ , BO ₃ , CO ₃ , F and NO ₃ anions,
0 <x <1, 0 <y ≦ 0.02, 0 <y ′ ≦ 0.02, 0.3 ≦ a ≦ 1.0, 0 ≦ b ≦ 0.7, and a + b = 1.

  The present invention also provides a method of manufacturing the secondary battery electrode.

Specifically, a method for producing the secondary battery electrode,
(I) a process of applying an electrode mixture containing an electrode active material on a current collector;
(Ii) preparing a solution containing an aluminum precursor;
(Iii) coating aluminum on the electrode mixture layer of step (i) through electrolysis using the solution of step (ii);
Can be included.

The aluminum precursor may be AlCl ₃ , but is not limited thereto.

  In the electrolysis in the step (iii), the aluminum precursor can be ionized with a solution for electrolysis and reduced to aluminum metal with an electrolytic electrode.

It is a schematic diagram of the electrolyzer based on one Example of this invention. 10 is a graph showing the results of Experimental Example 1.

  In this connection, FIG. 1 schematically shows an electrolyzer according to an embodiment of the present invention.

  Referring to FIG. 1, an electrolysis apparatus 100 includes a first roller 120 and a second roller 121 that roll a positive electrode sheet, an electrolytic solution 102 that contains an aluminum precursor, an electrolytic bath 101 that contains the electrolytic solution 102, and an electrolytic solution. 102, a reference electrode 110 made of Li or a hydrogen reference electrode to separate two or more metals contained in 102, a positive electrode 122 made of carbon material that oxidizes Cl, a first battery 109 that supplies current to the positive electrode 122, electrolysis A second electrode for supplying current to the negative electrode 106 and the negative electrode 106 of the lithium secondary battery positive electrode material, which is located inside the cell, reduces Al and deposits on the surface of the positive electrode sheet, and rolls the positive electrode sheet inside the electrolytic cell. It consists of a battery 108.

  The positive electrode 122 is supplied with a voltage of 4.5 V compared to lithium from the first battery 109, the negative electrode 106 is supplied with a voltage of 1.4 V compared to lithium from the second battery 108, and the positive electrode sheet is electrolyzed by the first roller 120. The moving roller placed inside the tank 101 and positioned inside the electrolytic cell 101 moved the positive electrode sheet inside the electrolytic cell 101, and the positive electrode sheet was reduced by the negative electrode 106 positioned at the lower end of the electrolytic cell 101. After Al is coated on the surface, it is wound around a second roller 121 located outside the electrolytic cell 101 through a moving roller.

In the positive electrode, Cl (g) + 2e ⁻ → Cl ⁻ reaction occurs, Cl ⁻ ions are oxidized, and in the negative electrode, Al ³⁺ (g) + 3e ⁻ → Al reaction occurs, and Al is deposited to coat the surface of the positive electrode sheet. Is done.

On the other hand, as described above, in the secondary battery electrode according to the present invention, an electrode mixture coated with aluminum (Al) and / or alumina (Al ₂ O ₃ ) is applied on the electrode current collector. The present invention provides a secondary battery including an electrode. At this time, the secondary battery may be a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery.

  In one specific example, the lithium secondary battery is generally composed of a positive electrode, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and a lithium salt-containing non-aqueous electrolyte, and other components of the lithium secondary battery. Will be described below.

  Generally, a positive electrode is manufactured by applying an electrode mixture, which is a mixture of a positive electrode active material, a conductive material, and a binder, onto a positive electrode current collector, and then drying, and if necessary, further adding a filler to the mixture Sometimes.

The positive electrode active material includes a layered compound such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ) in addition to the lithium transition metal oxide represented by the chemical formula 1 or 2, and one or more Compounds substituted with transition metals; chemical formula Li _{1 + x} Mn _2−x O ₄ (where x is 0 to 0.33), lithium manganese oxides such as LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; lithium Copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ ; chemical formula LiNi _1-x M _x O ₂ (where, M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3). Formula _{LiMn 2-x M x O 2} ( where a M = Co, Ni, Fe, Cr, Zn or Ta, is x = 0.01 to 0.1) or _Li 2 _Mn 3 MO ₈ (wherein M = Fe, Co, Ni, Cu, or Zn); a lithium manganese composite oxide represented by LiNi _x Mn _2−x O ₄ ; a lithium manganese composite oxide having a spinel structure represented by LiNi _x Mn _2−x O ₄ ; May include LiMn ₂ O ₄ partially substituted with alkaline earth metal ions; disulfide compounds; Fe ₂ (MoO ₄ ) _3, etc., but is not limited thereto.

  The positive electrode current collector is generally manufactured to a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired The surface of carbon or aluminum or stainless steel that has been surface-treated with carbon, nickel, titanium, silver, or the like can be used. The current collector can also form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, nonwoven fabrics, etc. Is possible.

  The conductive material is usually added at 1 to 50% by weight based on the total weight of the mixture containing the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without inducing chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black, acetylene black , Carbon black such as ketjen black, channel black, furnace black, lamp black, thermal black, etc .; conductive fiber such as carbon fiber and metal fiber; metal powder such as carbon fluoride, aluminum, nickel powder; zinc oxide, titanic acid Conductive whiskers such as potassium; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives can be used.

  The binder is a component that assists the binding between the active material and the conductive material and the current collector, and is usually added at 1 to 50% by weight based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer ( EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, various copolymers and the like.

  The filler is selectively used as a component that suppresses the expansion of the positive electrode and is not particularly limited as long as it is a fibrous material without inducing a chemical change in the battery. For example, polyethylene, polypropylene, etc. Olefin polymer: Fibrous materials such as glass fiber and carbon fiber are used.

  The present invention also provides a secondary battery including an electrode, and the secondary battery may be a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery.

  The negative electrode is manufactured by applying a negative electrode active material on a negative electrode current collector, drying and pressing, and may optionally further include a conductive material, a binder, a filler, and the like as described above. .

Examples of the negative electrode active material include carbon such as non-graphitizable carbon and graphite-based carbon; Li _x Fe ₂ O ₃ (0 ≦ x ≦ 1), Li _x WO ₂ (0 ≦ x ≦ 1), Sn _x Me _{1− x} Me ′ _y O _z (Me: Mn, Fe, Pb, Ge; Me ′: Al, B, P, Si, Group 1, Group 2, Group 3, Halogen of the Periodic Table; 0 <x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8), etc .; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ Metal oxides such as O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , Bi ₂ O ₅ ; conductive polymers such as polyacetylene Li-Co-Ni-based material; titanium oxide; use lithium titanium oxide In detail, the carbon-based material and / or Si may be included.

  The negative electrode current collector is generally manufactured to a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, A surface of calcined carbon, copper or stainless steel, which is surface-treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. Also, like the positive electrode current collector, it is possible to reinforce the binding force of the negative electrode active material by forming fine irregularities on the surface, such as films, sheets, foils, nets, porous bodies, foams, nonwoven fabric bodies, etc. It can be used in various forms.

  As the separation membrane, a thin insulating thin film having high ion permeability and mechanical strength is used between the positive electrode and the negative electrode. Generally, the pore size of the separation membrane is 0.01 to 10 μm and the thickness is 5 to 300 μm. As such a separation membrane, for example, a chemically resistant and hydrophobic olefin polymer such as polypropylene; a sheet or a nonwoven fabric made of glass fiber or polyethylene is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte can also serve as a separation membrane.

  The lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and lithium. As the non-aqueous electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used. Absent.

  Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1 , 3-Dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, propion It can be used aprotic organic solvent such as ethyl.

  Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, aggregation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and heavy ions containing ionic dissociation groups. Coalescence etc. can be used.

As the inorganic solid electrolytes, for _{example, Li 3 N, LiI, Li} 5 NI 2, Li 3 N-LiI-LiOH, LiSiO 4, LiSiO 4 -LiI-LiOH, Li 2 SiS 3, Li 4 SiO 4, Li 4 SiO _{4 -LiI-LiOH,} Li nitrides such as _{Li 3 PO 4 -Li 2 S-} SiS 2, halides, etc. can be used sulfate.

Lithium salt is a substance that is easily dissolved in a non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _6. LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylborate, imide, and the like can be used.

  For the lithium salt-containing non-aqueous electrolyte, for the purpose of improving charge / discharge characteristics and flame retardancy, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexalin Acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like may be added. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart incombustibility, and a carbon dioxide gas may be further included to improve high-temperature storage characteristics. Further, FEC (Fluoro-Ethylene Carbonate), PRS (Propene sultone), and the like can be further included.

In one embodiment, a lithium salt such as LiPF ₆ , LiClO ₄ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , EC or PC cyclic carbonate as a high dielectric solvent, and DEC, DMC as low viscosity solvents. Or it can add to the mixed solvent with the linear carbonate of EMC, and lithium salt containing non-aqueous electrolyte can be manufactured.

  The present invention provides a battery module including the above-described secondary battery as a unit battery, a battery pack including the battery module, and a device including the battery pack as a power source.

  At this time, specific examples of the device include a power tool that is powered by a battery motor; an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in Electric vehicles including a hybrid electric vehicle (Plug-in Hybrid Electric Vehicle, PHEV), etc .; an electric bicycle (E-bike), an electric motorcycle including an electric scooter (E-scooter); an electric golf cart (electric golf cart); However, the present invention is not limited to this.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the scope of the present invention is not limited thereto.

<Example 1>
0.5Li ₂ MnO ₃ * 0.5LiNi _0.32 Mn _0.32 Co _0.24 O ₂ was used as an active material, and conductive material (Denka black) and binder (PVdF) were respectively 95: 2.5: 2. The mixture mixed in NMP at a weight ratio of 0.5 was coated on 20 μm thick aluminum foil, and the rolled and dried electrode sheet was dissolved with AlCl ₃ as an aluminum precursor and ZnCl _{2 as a} catalyst. After being put into the electrolytic solution, electrolysis was performed for the reduction of aluminum, and a coating layer having a thickness of 10 nm made of aluminum and alumina was formed on the mixture layer, thereby manufacturing a positive electrode.

  Moreover, as a negative electrode, a natural graphite / Si-based active material is used, and conductive material (carbon black), binder (SBR), and thickener (CMC) are each made into NMP at a weight ratio of 94: 2: 3: 1. The mixture prepared by mixing was coated on a 20 μm thick copper foil, rolled and dried to produce a negative electrode.

An electrode assembly was manufactured using a porous separation membrane made of polyethylene (PE) between the negative electrode and the positive electrode thus manufactured. After placing the electrode assembly in a pouch-type case and connecting the electrode leads, an electrolyte solution containing LiPF ₆ 1M and ethylene carbonate (EC) / ethyl methyl carbonate (EMC) at 1: 2 (volume%) was injected, Sealed to produce a lithium polymer battery.

<Comparative Example 1>
A lithium polymer battery was produced in the same manner as in Example 1 except that the electrode sheet was not electrolyzed with an electrolytic solution.

<Comparative example 2>
A lithium polymer battery was produced in the same manner as in Example 1 except that the thickness of the coating layer was 200 nm.

<Experimental example 1>
In order to confirm the cycle characteristics of the lithium polymer batteries manufactured in Example 1 and Comparative Examples 1 and 2, a charging current density of 0.33 C, a charging voltage of 4.2 V, and a CC-CV (Constant Current-Constant Voltage), 5 A charge / discharge test was performed 100 times by charging under the condition of% current cut-off (cut-off) and discharging with a discharge current density of 0.33 C, a discharge voltage of 2.5 V, and a voltage cut-off (cut-off). The capacity change rate during the 100-cycle test was measured and is shown in FIG. 2 below.

  Referring to FIG. 2, in the case of the lithium polymer battery of Example 1 in which aluminum and alumina were coated on the positive electrode mixture layer with a thickness of 10 nm, Comparative Example 1 in which no coating layer was formed on the positive electrode mixture layer. It can be seen that it has improved lifetime characteristics and high reversible capacity as compared to the lithium polymer battery. On the other hand, it can be seen that the lithium polymer battery of Comparative Example 2 in which aluminum and alumina are coated thicker than the lithium polymer battery of Example 1 has a very low reversible capacity, despite the improvement of the life characteristics. This is because the thick coating layer largely suppresses the reaction of the electrode active material applied to the mixture layer with the electrolytic solution, and also suppresses the movement of lithium ions, and thus has a low capacity.

  A person having ordinary knowledge in the field to which the present invention belongs can make various applications and modifications within the scope of the present invention based on the above contents.

As described above, since the electrode for a secondary battery according to the present invention has a coating layer containing aluminum (Al) and / or alumina (Al ₂ O ₃ ) formed on the electrode mixture layer, Not only can the electrode active material react with the electrolyte under a high voltage, but also the conductivity of the electrode active material can be improved through a highly conductive Al coating. Further, Al that easily reacts with oxygen is converted into Al ₂ O ₃ by removing oxygen in the electrode, and the transition metal contained in the electrode active material can be fundamentally prevented from being deposited on the surface of the electrode. There is an effect.

DESCRIPTION OF SYMBOLS 100 Electrolyzer 101 Electrolysis tank 102 Electrolyte 106 Negative electrode 108 2nd electrode 109 1st electrode 110 Reference electrode 120 1st roller 121 2nd roller 122 Positive electrode

Claims (7)

An electrode mixture layer containing an electrode active material is coated on an electrode current collector, and the electrode active material is a lithium transition metal oxide represented by the following chemical formula 1 or 2, and the electrode mixture layer The coating layer made of aluminum (Al) and alumina (Al ₂ O ₃ ) is formed in an area larger than 50% of the area of the electrode mixture layer ,
The coating layer, characterized in that it is formed in a thickness of less than 0.5nm over ~ 100 nm, the lithium-ion battery or a lithium polymer battery electrode for a secondary battery:
_{Li x M y Mn 2-y} O 4-z A z (1)
In the above formula,
M is selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti, and Bi 1 Two or more elements,
A is one or more anions of -1 or -2 valence,
0.9 ≦ x ≦ 1.2, 0 <y <2, 0 ≦ z <0.2,
(1-x ′) LiM′O _{2-y ′} A ′ _{y ′} −x _′ Li ₂ MnO _{3-y ″} A ′ _{y ″} (2)
In the above formula,
M 'is a _Mn a _{M b,}
M _b is one or more selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr and Zn,
A ′ is one or more selected from the group consisting of PO ₄ , BO ₃ , CO ₃ , F and NO ₃ anions,
0 <x ′ <1, 0 ≦ y ′ ≦ 0.02, 0 ≦ y ″ ≦ 0.02, 0.3 ≦ a ≦ 1.0, 0 ≦ b ≦ 0.7, and a + b = 1.   The electrode for a secondary battery according to claim 1, wherein the electrode is a positive electrode. A secondary battery comprising the electrode according to claim 1 . A battery module comprising the secondary battery according to claim 3 as a unit battery. A battery pack comprising the battery module according to claim 4 . A device comprising the battery pack according to claim 5 as a power source. The device according to claim 6 , wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage system.

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